FIG. 1 is a simplified block diagram of a typical multi-user transmitter. Data b1(i) to bx(i) for each user, user 1 to user x, is turbo encoded by respective turbo encoders 101 to 10x. Although each data stream b1(i) to bx(i) is described as going to a different user, multiple or all (such as in the uplink) of the streams may be going to the same user. The output of the turbo encoders d1(j) to dx(j) are interleaved by respective interleavers (Πs) 121 to 12x. The interleaved outputs e1(k) to ex(k) are mapped to symbols, such as quadrature phase shift keying (QPSK) or quadrature amplitude modulation (QAM) symbols, by respective symbol mappers 141 to 14x. The symbols f1(l) to fx(l) are spread by respective speaders 161 to 16x. The transmit power level of the spread data is controlled by respective amplifiers 181 to 18x, having respective gain values of A1 to Ax. The amplified spread data is combined, such as by an adder 20. The combined signal is radiated by an antenna 22 or antenna array through an air interface to the respective users.
FIG. 2 is a simplified block diagram of a typical multi-user receiver. After radiation through the air interface, the combined signal is received by an antenna 24 as a received vector r. The received vector is processed by a joint detector 26 to produce an estimate of the original interleaved turbo encoded data Λ1[c1(1)] to Λ1[cx(1)] for each user, as soft values. The interleaved data is deinterleaved by respective deinterleavers (Π−1 s) 281 to 28x. The deinterleaved data is processed by respective turbo decoders 301 to 30x, producing respective estimates of the original data ĉ1(i) or ĉx(i). If only one or multiple ones of the original data streams b1(i) to bx(i) were intended for the receiver of FIG. 2, typically, the interleaved data for the other users would not be processed by the receiver.
To meet the demands for higher data rate services, it is desirable to have receivers with higher performance. Illustrations of channels facilitating higher data rate services are the high speed channels of the high speed packet data access (HSDPA) of the Universal Telecommunications System (UMTS) Terrestria Radio Access (UTRA) system and high speed channels of CDMA2000 EVDV. Accordingly, it is desirable to have alternate receiver designs.